Hey Tim, I would say 3 1/2 to 3 3/4 is close on the main needle. I have run several of the Ninja .21 and its about there and hardly have I had to adjust on it. Make sure on the 1/4, 1/2 and wot tanks you get it around 180-200 to make sure everything get nice and hot because these engine have alot of pinch. Kevin